Combustion turbines, such as gas turbine engines, generally comprise a compressor section, a combustor section, a turbine section and an exhaust section. In operation, the compressor section can induct and compress ambient air. The combustor section generally may include a plurality of combustors for receiving the compressed air and mixing it with fuel to form a fuel/air mixture. The fuel/air mixture is combusted by each of the combustors to form a hot working gas that may be routed to the turbine section where it is expanded through alternating rows of stationary airfoils and rotating airfoils and used to generate power that can drive a rotor. The expanding gas exiting the turbine section can be exhausted from the engine via the exhaust section.
The fuel/air mixture at the individual combustors is controlled during operation of the engine to maintain one or more operating characteristics within a predetermined range, such as, for example, to maintain a desired efficiency and/or power output, control pollutant levels, prevent pressure oscillations and prevent flameouts. In a known type of control arrangement, a bulk turbine exhaust temperature may also be monitored as a parameter indicative of a condition in the combustor section. For example, a controller may monitor a measured turbine exhaust temperature relative to a reference temperature value, and a measured change in temperature may result in the controller changing the fuel/air ratio at the combustor section.
In a known temperature monitoring system for controlling combustion operations, temperature monitors, such as thermocouples, are located directly in the exhaust flow of the turbine. Such monitoring systems generally require locating thermocouples at different fixed axial locations along the exhaust flow, which may introduce uncertainties in relation to temperature calculations for controlling the engine as conditions affecting operation of the engine change, such as a varying load condition on the engine. Providing temperature measurements of the hot working gas upstream of the turbine section has proven problematic due to difficulties in providing a sensor system capable of providing accurate temperature measurements on a long term basis in this region of the engine.